I am an A-player with a problem of how to develop an effective study system for continuous improvement (at a rapid pace).

Based
on some books and articles I have read and some advice from higher
level players (experts, masters, etc.) they say that focusing more on
tactics and endgames (and I would like to add pawn play to that list)
will help you improve your game faster, while others (experts, masters,
GMs) suggested that I work more on openings.

From my experience (which is very brief) I noticed that more
recently that although my game has shown some improvement -
(particularly against experts and sometimes against masters) - from
trying to do both, I also noticed that some of my games I do not finish
efficiently, lose advantages gained from the opening, or sometimes I
get completely taken out of "my game" in the opening.

What would
you recommend my approach be to solve that problem quickly? (I cannot
dedicate all my time to chess because I have a full time job and have
other career endeavors - but I still think that if I do a little each
day with chess it will still add up.)

J.W.

I get this kind of question a lot but seldom answer it because I cannot really offer the readers what they want. I can't really evaluate which advice you have received works best for YOU, because I don't know enough about your strengths and weaknesses. There is no surefire program for improvement, and different courses of study will work for different players. It's up to the individual to make certain decisions. You can try to balance your work (e.g. some openings, some tactics, some endgames), you can study to bolster your weak points, or you can try to accentuate your strengths.

Openings become increasingly important as your level rises. I think at Class A, you still have a lot more to learn about strategy. Studying openings is probably the best way to improve your results in the short-term, but insufficient to raise your level for the long haul without strengthening your knowledge of strategy.